Ma Sœur Aînée
by Mythril Moth
Summary: Chat Noir decides to follow Nathalie around town on her day off to see what she does in her spare time.


**Author's Notes:**

A little something that started with a silly, playful notion and, as many of my stories are wont to do, went somewhere I was not expecting.

Enjoy!

* * *

 **MIRACULOUS LADYBUG: "MA SŒUR AÎNÉE"**

 _by Mythril Moth_

Adrien Agreste was bored.

It was a rare weekend that Adrien didn't have anything scheduled—no extra lessons, no photo shoots, nothing. Father was in Milan visiting an old friend, and—probably at Nathalie's insistence—he had decided to give Adrien an entire weekend of free time. This was no doubt due to the fact that this was Nathalie's weekend off, the one weekend each month she took as personal time.

Ordinarily, Adrien was thrilled to get time to himself, especially a whole weekend. He could go to the cinema, hang out with his friends, or just relax and turn his attention to one of his favorite topics: Ladybug, and the quest to deduce her identity.

But he wasn't in the mood to see any of the movies that were playing this weekend, he didn't really feel like sitting in front of his computer daydreaming, and his friends all had plans with family (and forget hanging out with Chloé, he would never be _that_ bored).

He stood by the window, watching as Nathalie slung a medium-sized tote bag into the trunk of her car. "I wonder what she even _does_ with her weekend off," he mused absently.

"Well, she's not a terribly interesting person, so I imagine she doesn't do anything terribly exciting," Plagg said.

"Hmm." Adrien stroked his chin contemplatively. "What do you say we find out? **Plagg, claws out!** "

Before he could protest, Plagg was sucked into the silver ring on Adrien's right hand, which turned glossy black. Green bands of magical energy swept over Adrien's body, replacing his clothes with a skintight black leather catsuit, complete with clawed gloves, a belt that served as a faux cat tail, a pair of leather cat ears atop his now wild and unruly blond hair, a black leather mask over his eyes, which went from warm, verdant green to bright, luminescent cat eyes, and a little jingle bell on his collar. A silver-black baton appeared at his hip.

With a smirk, Chat Noir detached and extended his baton, using it to follow Nathalie Sancoeur's car as she left the Agreste estate.

* * *

 _"Ouvre les yeux, imagine un monde, ouvre les yeux, a chaque seconde..."_ Nathalie sang along with the car stereo, idly drumming her fingertips on the steering wheel as she smoothly navigated through traffic. Unaware of the black shadow following her high above the street, she pulled into the car park that serviced the fitness club she belonged to. She removed the tote from the trunk, slung it over her shoulder, and ascended to street level, walking the block and a half to the fitness club.

The receptionist greeted her; she showed her membership pass, then headed through the maze of exercise machines and morning fitness buffs, wending her way toward the locker rooms. Ten minutes later, she emerged wearing tight black knee-length shorts, black sweatsocks, white tennis shoes, and a dark purple tank top. Protective goggles hung from a nylon strap around her neck, and she lightly bounced a racquet against one shoulder as she headed upstairs to the club's racquetball courts, which provided a spectacular view of the city through windows which ran the entire length of the outside wall, protected by a thin, tinted plexiglass guard. There, she met Nadja Chamack, similarly attired but in wine red.

"Ready to lose?" Nadja taunted.

Nathalie secured her goggles over her glasses. "I believe I've won the last five matches," she said coolly, offering a faint smirk as the two women entered a free court.

* * *

Using the zoom function of his baton, Chat Noir watched Nathalie and Madame Chamack play a heated racquetball match. "Wow," he muttered to himself. "I've _never_ seen Nathalie sweat before. I didn't even know she _could_ sweat..."

The match went on for an hour and a half, during which Chat Noir played the part of Nathalie's silent, secret cheering section. She just barely won by a single point in the fifth game of a best-of-five series, after which the women left the court. Chat Noir smiled. "That was intense," he said. He sat back with a sigh. "Guess I'll have to wait until she leaves to see what else she gets up to..."

He didn't have long to wait, as it turned out. Less than twenty minutes later, Nathalie was back on the road again; smirking, he bounded after her car as she made her way to the Champs-Élysées. Once again, she parked her car in a car park; she spent the better part of an hour wandering in and out of stores, only occasionally emerging with a purchase. Keeping tabs on her here was tricky, as inevitably he was spotted, pointed out, and had phone cameras pointed at him while he ghosted Nathalie along the busy avenue. At one point, he spotted his classmate and friend Marinette walking along the Champs with her mother and an older woman he didn't recognize; as he was shifting his position so as not to lose Nathalie, he caught Marinette's eyes, which widened in surprise as she looked right at him. He grimaced as he saw her have a rushed, frantic conversation with her mother before ducking out of sight and disappearing.

No doubt she went to call Alya. Then this would wind up on Ladyblog, and the next time he saw Ladybug he'd have to explain—

"What's going on, Chat Noir? What are you doing roaming up and down the Champs-Élysées? You didn't see an Akumatized, did you?"

Chat Noir stiffened, his tail extending straight out behind him. He turned around, his wide green eyes landing on Ladybug, who stood behind him on the roof where he was currently perched. "Oh, uhh...hey Bugaboo," he said nervously. "F-fancy running into you here! Haha..."

Ladybug narrowed her eyes. "You're up to no good, aren't you?"

"Why-why I would _never_ , My Lady!"

Ladybug crossed her arms and tapped her foot. "Alright. So why are you running around up here?"

 _*Better come up with something that isn't an obvious, total lie. Ladybug gets_ _ **super pissed**_ _at liars...*_ Chat Noir decided to tell at least part of the truth. Letting out a sigh, he relaxed his posture. "Honestly? I am _phenomenally_ bored today, so I'm just out doing some people-watching. You know...superhero-style." He smiled disarmingly.

Ladybug pursed her lips. "Huh. So...nothing going on, no Akumatized, nobody's in trouble? You're just bored?"

"Yep! Just bored. Sorry if I startled you." An idea struck him, and he grinned cheekily. "Of course, now that _you're_ here—"

He didn't even get to finish before Ladybug threw her yo-yo and launched herself across the street, disappearing behind a building on the other side. Chat Noir contemplated following her, but three things stopped him.

One: She was probably aggravated with him now.

Two: She probably had her own thing going on and he'd dragged her away from it.

Three: Nathalie was headed back in the direction of the car park.

Sighing, Chat Noir crouched low and ran along the rooftops, ready to follow Nathalie to her next destination.

* * *

"I can't believe that _stupid_ tomcat!" Marinette growled as soon as she reversed her transformation.

"Hmm," Tikki muttered. "Well, it's not like there's anything _wrong_ with it." She smirked at Marinette. "Besides, you've used _your_ Miraculous for things that had nothing to do with protecting Paris before, remember?"

Marinette sighed. "Yeah, yeah," she grumbled. "It's just...if he wants to do some people-watching, couldn't he do it a little less conspicuously? I mean, he's attracting a _lot_ of attention to himself out there!"

"Just let it be, Marinette," Tikki said. "So what if he wants to stretch his legs a bit? It's not like Paris isn't used to seeing the two of you running around. Now come on, we need to get back to your mom and your aunt."

"You're right." Marinette shook her head. "Crazy alley cat..."

* * *

After ditching her car at yet another car park, which led Chat Noir to wonder why she was even bothering driving, Nathalie—a different, smaller bag slung over one shoulder—walked into Tom & Sabine Boulangerie-Patisserie, then came out a few minutes later with a medium-sized paper bag. Chat Noir raised an eyebrow at that. _*Nathalie has a sweet tooth?*_

From there, she walked to Le Grand Paris. Chat Noir frowned as she entered the hotel. "Hmm. Wonder what she's doing there? Is she meeting somebody? A friend? A lover? No, that's absurd..." He shook his head. "Well, I guess the only way I can find out is to go inside, but..."

He remembered Ladybug's expression of exasperation earlier, and winced. "Yeah, that's not gonna work. And if I go in as Adrien, she'll know I'm following her _and_ I risk having to deal with Chloé..." He sighed. "Well, I guess this is as far as _this_ hunt goes." Shaking his head, he vaulted onto the roof of the hotel. Landing nimbly on the balustrade, he looked over the pristine, sparkling pool and the neatly arranged pool chairs. He flicked a hand through his hair and smirked. "Might as well take a load off." Tail twitching behind him, he made his way to one of the pool chairs and stretched out, folding his arms behind his head. "I'm sure Mayor Bourgeois won't mind."

Several minutes passed. Chat Noir felt sleepy in the warm sun. He'd just closed his eyes for a catnap when the roof elevator dinged. He tensed, glancing warily at the elevator as it opened...

His jaw dropped.

Nathalie Sancoeur stepped out onto the roof wearing a high-cut, strapless white bikini and matching sandals. In one hand, she held her smaller bag and a bottled water; in the other, she held the paper bag she'd left the boulangerie with. A towel was slung across her shoulders. As soon as she saw him sprawled on one of the pool chairs, she stopped still and blinked.

 _*Holy...crap...*_ Mouth dry and heat rising to his cheeks, Chat Noir weakly raised a hand and waved. "Hi?"

"Umm...hello?" Nathalie ventured. She frowned, looking around warily. "Is...is there a monster?"

"No! No, I mean...no, everything's peaceful," Chat Noir said, sitting up and smiling awkwardly, trying not to stare and failing miserably. _*Wow. Just...wow.*_ Nathalie was not the most curvaceous woman in Paris, but that bikini made Chat Noir aware of just how feminine and how _incredibly_ attractive she was. Coughing and ducking his head, he added, "Umm...I was just out...patrolling! For, y'know...stuff. And decided to stop and take a break." He laughed sheepishly.

"Oh." Nathalie pursed her lips and tilted her head curiously. "Aren't you roasting alive in that?"

"Huh? Oh! No. It's magic, it's...I know it looks like, y'know, but it's...it breathes."

"I see." Nathalie shifted awkwardly. "Well, I..."

"Oh, don't mind me!" Chat Noir said hastily. "Just go about whatever you were doing. Umm...unless you want me to leave?" _*Knowing Nathalie, there's no way she'd ever want anybody to see her like this...*_

Nathalie adjusted her glasses. "No, that won't be necessary," she said, moving to the pool chair next to Chat Noir's and sitting down. She set her things down and took a bottle of sunscreen out of her bag, applying it to her arms and legs. Chat Noir tried to look anywhere _but_ at her as she lotioned herself up.

And failed miserably.

Nathalie caught his red-cheeked glanced and snorted. "Enjoying the view?"

"Ah! S-sorry!" Chat Noir said in a strangled yelp. "I—I didn't mean to—"

"I'm not offended," Nathalie said in the same matter-of-fact tone in which she always dictated his schedule. "I do come up here to sunbathe for solitude, but it's inevitable that I'll occasionally have company, sometimes male, occasionally interested in looking at my body. You appear to be a teenager, so it's only natural."

"Uhh..." Chat Noir shook his head frantically. "Y-yeah, but..." He coughed. "A-anyway."

"I'm surprised you'd even have such a reaction, honestly," Nathalie continued dispassionately as she rubbed lotion on her thighs. "I'd think spending so much time around Ladybug, a woman in a bikini wouldn't even get a rise out of you, non?"

Chat Noir spluttered. "Wh-what?!"

"Well, it's just that her outfit, it's quite...form-fitting."

Chat Noir's entire face burned crimson. "Let's... _not_ talk about that right now, please?"

Nathalie smirked, clearly amused. "I see," she said. Once she finished applying her sunscreen, she wiped her hands on her towel, which she folded on the floor beside her. She opened the paper bag and extracted an eclair. She glanced at Chat Noir. "Would you like an eclair? Or a macaron? I have several different items."

"Umm..."

"I always buy more than I'll ever conceivably eat," Nathalie assured him. "Go ahead, help youself."

"A-alright." Chat Noir reached into the bag and pulled out a couple of macarons. "Why do you...I mean, why buy so much if—"

"It doesn't go to waste," Nathalie said. "I always know one or two people I can give any extra to. Or I share it if I encounter anyone here." She bit into her eclair and let out a little moan of delight which sent shivers up Chat Noir's spine. "Mostly it's my way of saying thank you to the family that runs the shop."

"Oh?" Chat Noir asked, genuinely curious.

"Well...and partly as an apology." Nathalie grimaced. "Can...can I trust you? If I make a confession?"

Chat Noir couldn't help but flash a playful smirk at her. "Hey, this is a kitty collar, not a priest's collar," he joked. "But...sure, you can trust me. I won't let the cat out of the bag."

Nathalie peered oddly at him, her eyes and lips thinned. "Your sense of humor is terrible," she said bluntly.

"So I've been told," Chat Noir said. "Anyway, you were saying?"

Nathalie studied him, then sighed. "Well...you know I work for Monsieur Agreste, right?" At Chat Noir's nod, she shifted to lie back on the pool chair, gazing up at the sky. "He is...not the easiest man to work for. Doubly so when...well..." She sighed. "Perhaps I shouldn't say too much."

"No, it's...it's fine." _*I know better than anyone how hard Nathalie works. If she's so pent up and alone that she has to turn to a random superhero to vent...*_

"It's just...Monsieur Agreste has put me in charge of micromanaging his son's life to a ridiculous degree. If...if _she_ were still around, she would _never_ allow some of the insane things..." Nathalie grimaced. "Well, no, it was pretty bad even before, but at least with her around, he wasn't..." She shook her head.

Chat Noir fought to hide his pained wince. "Adrien misses his mother very much," he said roughly. "I know."

Nathalie glanced at him, startled. "How?"

"Oh! Um, well...I've met him a few times, yeah? I mean, his school gets hit by Akumatized a lot, and then there was that whole mess with Jackady."

"Oh...of course." Nathalie sighed. "How much has he told you?"

"Well...enough," Chat Noir hedged. "Missing mom, emotionally distant and overbearing dad..." He shrugged. "That's all I know."

"It's only since he forced the issue of wanting to go to school with other kids that he's actually started making friends and even being remotely happy," Nathalie said. "I...I try to keep an emotional distance. My job isn't to...isn't to be a replacement for his mother. My job is to make schedules and handle whatever Monsieur Agreste needs handled. I can't...I have to try not to be part of the drama, you know?" She shook her head. "Not that that's possible, not in that house."

Chat Noir felt a heavy weight settle in his stomach. _*Merde...I never even thought about how hard it must be for Nathalie, being caught between me and my father like this...*_

"Anyway...confession," Nathalie said. "Adrien has a friend, a girl who lives at that boulangerie. She seems to be very nice, very kind. If...if his mother were still around, I wouldn't put it past her to try matching them together."

Chat Noir blinked. _*Maman would...try to set me up with Marinette?*_

"Well, Adrien's last birthday was...pretty tense. He wanted to have a birthday party, Monsieur Agreste refused, Adrien's best friend decided to press the issue... _that_ went badly, Adrien's friend was Akumatized—"

"The Bubbler."

"Right." Nathalie adjusted her glasses. "Well, the thing is, Monsieur Agreste ordered me to pick up a birthday present for Adrien at the absolute last minute. If he'd given me some notice, or...or actually done it himself..." Her voice became rueful, reproachful. "Well, I sort of panicked."

Chat Noir frowned. _*But wait, no...Father gave me that scarf...it had to have taken days, weeks to knit...*_

"You see, before the whole incident with the Bubbler, Adrien's friend Marinette, she dropped off a present for him. When Monsieur Agreste, when he was angry at me because I hadn't anticipated his order to buy Adrien a present, I..." Nathalie sighed. "I took Marinette's name off the present and gave it to Adrien, told him it was from his father."

Chat Noir's eyes widened. _*The scarf...it was from Marinette? But...why didn't she say anything? Mon Dieu...*_ "And...and he never found out the truth?"

"As far as I know, no." Nathalie shook her head. "I should never have done it. If I had it to do over again, I wouldn't."

"So...you buy huge piles of sweets from her parents because you feel guilty about that?"

"In part," Nathalie said. "I mean...I can't just confess what I did. If I break Adrien's trust in me, he'll really be all alone in that house. I can't...I don't want to think about what would happen if he felt like there wasn't anybody in his home he could trust."

Chat Noir flinched, remembering his little tantrum on Christmas that led to Ladybug assaulting an innocent Father Christmas and the resulting Akumatized.

"But also, it's..." Nathalie paused. "Tom and Sabine, they...they ask about Adrien. They care about him. I don't know how much they know, but...I get the impression they know enough to worry, and they ask about him. So...I make sure to buy a lot from them whenever I have a weekend off, to thank them...for caring."

Chat Noir felt tears well up in his eyes. Marinette's parents were amazing, he knew that. He didn't know they were _that_ amazing.

"My apologies," Nathalie said, her tone suddenly stiff and businesslike again. "Here I am, burdening you with all my problems when you have an entire city to worry about."

Chat Noir shook his head and looked at her, smiling. "I don't mind," he said. "Besides, it's good to get all that out, non? Carrying around too much tension, it's bad for the skin. It'd be a shame to let a pretty lady like you ruin her looks from too much stress."

Nathalie smiled. "I think I'm a little too old for you to flirt with, but thank you."

"Ah, but I have to protect my reputation as a Catsanova," Chat Noir said with a smirk, standing up and sketching a bow.

Nathalie shook her head. "I pity Ladybug, putting up with your jokes."

A distant explosion sent a huge plume of smoke into the sky. Chat Noir and Nathalie both tensed, staring in that direction. _"Merde,"_ Chat Noir hissed. "Well, it looks like I won't be basking in your beauty for the rest of the day after all, Mademoiselle," he said. "If I'm not mistaken, _that_ was a cat call." Detaching his baton from his belt, he sprinted for the edge of the roof and leapt off.

Nathalie sighed, pulled out her phone, and checked for a live news stream. "And I was about to ask him for a back massage," she muttered. "Those claws would've been perfect for shiatsu..."

* * *

Sunday evening found Adrien sitting in his room playing a newly released video game. Nathalie knocked on the door, waited precisely ten seconds, then entered. "I've prepared your schedule for the week," she said. "I think we should review it now."

Adrien paused his game. "How was your weekend?" he asked.

Nathalie pressed her lips thin. "It was productive," she said.

Adrien rolled his eyes. "It was your weekend off," he said. "Was it _relaxing?_ "

Nathalie frowned. "I don't see how that's relevant—"

Adrien stood up. "I'm just making sure you take time to unwind," he said. "You work harder than anyone I know, and dealing with me and Father both can't possibly be easy. I just, y'know..." He offered a wan smile. "I care."

Nathalie blinked. "Oh," she said, nonplussed. "Well." She adjusted her glasses. "Yes, I...I found time to unwind this weekend. I played racquetball with a friend, I...did a little sunbathing by the pool..."

"Sounds like fun," Adrien said. "You know, if you ever need to put down the tablet and phone and just...talk, for a few minutes, or if you want to take a break and play a game or something, I'm always here. You don't have to wait for that one weekend a month to relax a little."

Nathalie pursed her lips. "I don't know if that's appropriate—"

Adrien snorted. "Because you're Father's assistant?" He shook his head. "You don't have to act like an emotionless robot all the time. It's okay to be human."

Nathalie was silent for a long moment. "I'll think about it," she said.

"It's a start," Adrien said. "Alright, let's go over that schedule." As he said so, he picked up a box from the boulangerie that sat on his desk. "Want an eclair? I bought more than I meant to, they just looked so good."

Nathalie blinked. "Y-yes, thank you," she said. And she sat down on the sofa with Adrien, reviewing his schedule and eating eclairs.

 _*You're right...you're not a replacement for my mother, nobody can ever be that. But if I'm very lucky, I can get you to think of yourself as, maybe...a really amazing big sister. One who's always looking out for me.*_

 **FIN.**

* * *

 _Miraculous Ladybug is the intellectual property of Zagtoon, Method Animation, Toei Animation, and Thomas ASTRUC. This intellectual property is used without permission with no intent to profit from said use. The unique content contained on this page is the property of Mythril Moth, and redistribution of this content without express permission is strongly discouraged._


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